Photo: DTU Fødevareinstituttet. Vævsprøve fra bugspytkirtel / Tissue sample from pancreas

Mixture of pesticides causes lower birth weight in rats

Monday 02 Jul 18


Sofie Christiansen
Senior Researcher
National Food Institute
+45 35 88 70 25


Terje Svingen
Head of Research Group, Associate Professor
National Food Institute
+45 93 51 88 80

Pregnant rats that are given a mixture of pesticides at doses that individually are not harmful, risk having offspring with lower birth weight, studies from DTU show.

In risk assessments, pesticides are generally evaluated one substance at a time. Assessments are based on the so-called NOAEL (No Observed Adverse Effect Level) value, which is the highest tested dose at which a chemical does not cause an adverse effect in animal experiments. However, in the real world, humans are exposed to multiple pesticides at once.

Studies have shown that certain pesticides can cause reduced birth weight. In both humans and animals, a low birth weight suggests that prenatal development has not been optimal. A low birth weight also increases the risk of obesity and disease later in life such as type 2 diabetes.

Until now, no studies have looked at the combination effects of pesticides that can cause reduced birth weight. A team at the National Food Institute, Technical University of Denmark, has now completed a research project funded by the Danish Environmental Protection Agency (EPA). They tested the effect of combining six EU-approved pesticides at doses that individually do not cause reduced birth weight. Three of the pesticides are approved for use in Denmark.

Cocktail effect was identified

In two different studies, each pesticide was added to the cocktail at a dose that in itself is not harmful. The rat offspring were then exposed to the cocktail both before birth via the placenta and after birth via the mother's milk. Both studies showed that the mixture reduced the birth weight even with individual pesticide doses significantly lower than NOAEL.

The study results support previous findings from animal studies, which show that exposure to mixtures of endocrine disruptors—including pesticides—can cause significant combination effects at doses where the individual substances have no adverse effect.

The offspring did not show clear signs of metabolic syndrome at 4-5 months of age. Metabolic syndrome is a collection of early symptoms for lifestyle diseases such as cardiovascular disease and type-2 diabetes. However, the fact that the young rats did not show clear signs of metabolic syndrome does not rule out that these effects can appear later in life.

Risk that cocktail effects are overlooked

The results from the two new studies indicate that current practices of carrying out risk assessments for one pesticide at a time based on NOAEL can underestimate the risk of causing lower birth weight. In order to account for any potential adverse effects of chemical mixtures, the researchers from the National Food Institute find that cumulative risk assessments are necessary.

The research team recommends including all types of chemicals that may lead to reduced birth weight, e.g. pesticides, industrial chemicals and environmental contaminants, to which humans may be exposed. 

Using current risk assessment protocols may underestimate the risk to humans. Although cumulative risk assessments of pesticides are used in Denmark, the combined exposure to different chemicals other than pesticides or from sources other than food are not accounted for.

Read more

The new studies are part of a research report the National Food Institute has prepared for the Danish EPA: Combination effects of pesticides on birth weight and metabolic programming in rat offspring. Danish Environmental Protection Agency’s Pesticide Research Programme has supported the work financially.

You can also read about the studies in two separate scientific journals: Combined exposure to low doses of pesticides causes decreased birth weights in rats, which has been published in the journal Reproductive Toxicology, as well as Effects on metabolic parameters in young rats born with low birth weight after exposure to a mixture of pesticides from the journal Scientific Report.
27 NOVEMBER 2021